Randonnée ski boots need to perform a number of different functions in order to serve their owners' needs. They must provide control over your skis for descending, but also be flexible, light and comfortable enough to skin, hike and climb well for hours on end.
To achieve this multi-purpose ideal, most modern randonnée boots are designed with light weight as a primary goal. They have a softer overall flex than alpine boots, a lugged sole with a slight curvature for hiking and climbing, and a lockable walking hinge that lets your ankle flex freely when not skiing. To achieve stiffness without adding weight, boot designers are increasingly moving away from the use of polyurethane (PU) and toward materials like Pebax and Grillamid, as well as substituting carbon fiber for various structural pieces of the boot. All this, of course, adds to the pricetag. High-end randonnée boots now typically run in the $700-$1,000 range and even higher.
Backcountry is hip these days, and the largest potential market lies with the "crossover" alpine crowd. The end result is, among other things, that manufacturers are concentrating on beefier boots that appproach alpine levels of stiffness and control but are still suitable for short to medium length touring. What's new is the trend toward installing tech fittings in said boots. This in turn is driving the trend toward higher DIN randonnée bindings, both tech and non-tech, and should continue to do so for the immediate future. Many of these products are suitable for strong skiers moving beyond the boundaries of the ski area, who feel more secure with alpine-type support.
I won't go deeply into "crossover" boots here - every alpine boot maker has a stiff performance boot (or several) with a walk mode that makes it more comfortable for booting and bearable for light skinning, but you'll want something with a better range of cuff motion if you plan on touring very far. The available range of true touring boots spans a wide range of weights and stiffnesses, from near-alpine flex boots like the Dynafit Vulcan and Mercury and the Scarpa Maestrale RS and Freedom SL to medium-flex boots like the Scarpa Maestrale 1.0, Dynafit TLT6 series, and La Sportiva Spectre. Add über-light race-oriented models like the Dynafit RC1, Scarpa Alien 1.0, and La Sportiva Stratos Cube and you've got something for every taste.
When you start doing longer trips and more vertical, it makes sense to put together a dedicated touring setup with a lighter boot that is designed for touring rather than lift skiing. Look for something that weighs less than 1,500 grams per foot with the smoothest and widest range of cuff motion you can find (assuming, of course, that you can get it to fit your foot). Both the lighter weight and the ability to make a longer stride while skinning will make a big difference.
As with skis and bindings, there is a trade-off between control while skiing (and the ability to drive longer, wider skis) and comfort and energy conservation while climbing and skinning. Experienced ski tourists are often willing to forgo some downhill control in favor of lighter weight and improved climbing - after all, the vast majority of their time is spent going uphill. The amount of downhill control a skier is willing to sacrifice is a personal decision - longtime expert alpine skiers used to alpine race or freeride boots may find it difficult to adjust to the softer randonnée boots right away, while people coming from a telemark or nordic background may find the control offered by a super light randonnée boot remarkable.
Thermo-formable boot liners (which are heated in a convection oven or with hot air, then placed in your boot and buckled up to mold to your foot) are highly desirable both for lightness and comfort; they can easily lighten the weight of a pair of boots by over a pound. Switching from stock to aftermarket liners is common among experienced skiers, and can completely transform both the fit and skiing properties of a boot - keep in mind that the style of liner also affects performance, with overlap liners generally providing more responsive ski performance and tongue liners generally better skinning flexibility.
As with any form of non-conforming plastic footwear, problems with protruding bony areas are best addressed by a professional boot fitter - it's not a cheap solution, but a good fitting boot with a custom footbed can do wonders for your skiing, not to mention your disposition. Prevailing wisdom has it that you should always buy the boot that fits best, and there is some logic to this. If you can find a boot that fits well (after baking the liner) and it happens to ski and skin well for you, so much the better. The flip side of the coin is that a good bootfitter can make almost any boot fit almost any foot, as well as adjust flex profiles and stance problems - many longtime skiers prefer to shop for a boot that has the flex pattern and features they want, even if it kills them in the shop, and take it immediately to their favorite bootfitter before skiing it.
© 2015 Gregory C. Louie